PERTH, Australia — Search planes scoured a remote patch of the Indian Ocean but came back empty-handed Friday after a 10-hour mission looking for any sign of the missing Malaysia Airlines jet, another disappointing day in one of the world’s biggest aviation mysteries.

Australian officials pledged to continue the search for two large objects spotted by a satellite earlier this week, which had raised hopes that the two-week hunt for the Boeing 777 that disappeared March 8 with 239 people on board was nearing a breakthrough.

But speaking at a news conference in Papua New Guinea, Australian Prime Minister Tony Abbott said, “We’ve been throwing everything we’ve got at that area to try to learn more about what this debris might be.”

And he admitted that the objects “could just be a container that’s fallen off a ship — we just don’t know.”

“So something that was floating on the sea that long ago may no longer be floating — it may have slipped to the bottom. It’s also certain that any debris or other material would have moved a significant distance over that time, potentially hundreds of kilometres.”

Pieces of an aircraft have been found floating for days after a crash into the ocean. Peter Marosszeky, an aviation expert at the University of New South Wales, said the plane’s wing could remain buoyant for weeks if the fuel tanks inside were empty and had not filled with water.

Other experts said that if the aircraft breaks into pieces, normally only items such as seats and luggage would remain floating.

“We seldom see big metal (pieces) floating. You need a lot of (buoyant) material underneath the metal to keep it up,” said Lau Kin-tak, an expert in aircraft maintenance and accidents at Hong Kong Polytechnic University.

A satellite image company said on Thursday that the sheer number of images covering a large swath of ocean contributed to the delay in identifying the debris and reaching the searching area.

DigitalGlobe Inc, a Colorado-based company that collects imagery for the U.S. government and other countries, as well as private companies, confirmed on Thursday that it had collected satellite images on March 16 that appeared to show debris that may be related to the disappearance of Malaysia Airlines Flight MH370.

It said it provided the images to Australian authorities, who released them earlier Thursday. DigitalGlobe said the Australian government had begun combing through the imagery of the current search area only in the last few days, after the massive international effort was expanded to the southern Indian Ocean region and waters near Australia.

Malaysian officials described the images as a credible sign of a possible wreckage from the flight, which left Kuala Lumpur on March 8.

“Given the extraordinary size of the current search area, the lengthy duration of the analysis effort was to be expected,” DigitalGlobe spokesman Turner Brinton said in a statement.

Brinton said the company’s five high-resolution satellites capture more than 3 million square kilometres of earth imagery each day. “This volume of imagery is far too vast to search through in real time without an idea of where to look,” he said.

Truss told reporters that two Chinese aircraft are expected to arrive in Perth on Saturday to join the search, and two Japanese aircraft will be arriving Sunday. A small flotilla of ships coming to Australia from China was still several days away.

“We are doing all that we can, devoting all the resources we can and we will not give up until all of the options have been exhausted,” Truss said. “We can’t be certain that the sightings are in fact debris from the aircraft (but) it is about the only lead that is around at the present time.”

The search area in the southern Indian Ocean is so remote it takes aircraft four hours to fly there and four hours back, leaving them only enough fuel to search for about two hours.

The owner of a Norwegian car carrier said it planned to search through the night for the two large objects sighted off Australia, despite the official search being suspended because it was too dark. The Hoegh St. Petersburg was the first ship to arrive in the area.

“We will continue searching during the night at reduced speed and with all spotlights available, and we will increase the speed again when the light comes back,” Ingar Skiaker, Chief Executive of Hoegh Autoliners, told a news conference in Oslo.

“We have not had any report of any finds, but if or when they find something… the captain will report to the Australian authorities first,” he said.

Three Chinese naval ships were heading to the area, along with the icebreaker Snow Dragon, Chinese state television reported. The icebreaker was already in Perth following a voyage to the Antarctica in January.

The Australian Maritime Safety Authority said search conditions improved Friday, with much better visibility than the previous day, but that the search “has concluded for today without any sightings.”

Malaysian Defence Minister Hishammuddin Hussein told reporters that “This is going to be a long haul.”

“The focus has always been to find the airplane and the focus is to reduce the area of search and possible rescue,” he said.

Hishammuddin said he would be speaking to U.S. Secretary of Defence Chuck Hagel later Friday “to request further specialist assets to help with the search and rescue efforts, including remotely operated vehicles for deep ocean salvage.”

John Young, manager of the maritime safety authority’s emergency response division, said the aircraft will head back on Saturday to the search zone, 2,300 kilometres from western Australia, but the area will change slightly depending on water movements overnight.

Abbott spoke with Chinese President Xi Jinping, whom he described as “devastated.” Of the 227 passengers on the missing flight, 154 were from China.

“It’s about the most inaccessible spot that you could imagine on the face of the Earth, but if there is anything down there we will find it. We owe it to the families of those people to do no less,” Abbott said.

The satellite discovery raised new hopes of finding the jet and sent another emotional jolt to the families of the people on board. The anguished relatives have been critical of Malaysian officials for delays in releasing information.

In Beijing, relatives met Friday with Malaysian officials at a hotel where most have been staying awaiting the latest news. Attendees said they had a two-hour briefing about the search but that nothing new was said.

One of the floating objects detected by the satellite was 24 meters (almost 80 feet) long and the other was 5 meters (15 feet).

Brinton said the satellite images were captured on March 16 by the company’s Worldview-2 satellite at a resolution of about 50 cm, and the company was continuing to collect imagery over the area where the possible debris had been spotted.

DigitalGlobe said it had been collecting images over a broader area than the official search area, while focusing the efforts of its crowdsourcing volunteers on the search areas identified by authorities. “The efforts of millions of online volunteers around the world allowed us to rule out broad swaths of ocean with some certainty,” Brinton said.

The hunt has had several false leads. Oil slicks that were seen did not contain jet fuel. A yellow object thought to be from the plane turned out to be sea trash. Chinese satellite images showed possible debris, but nothing was found.

Malaysian authorities have not ruled out any possible explanation for what happened to the jet, but have said the evidence so far suggests it was deliberately turned back across Malaysia to the Strait of Malacca, with its communications systems disabled. They are unsure what happened next.

Police are considering the possibility of hijacking, sabotage, terrorism or issues related to the mental health of the pilots or anyone else on board.